1. Field of the Invention
This invention relates generally to article handling and more specifically to an apparatus and method for unstacking articles with suction by removing the highest article first from a stack.
In the embodiment shown herein, the invention is used on an article of food, namely tortillas. Tortillas are unstacked and placed on a moving belt, spaced and separated from each other.
2. Prior Art
Certain articles of a flat, flexible form are stacked and then unstacked during their production or use. For instance, in the factory processing of tortillas, which are flat, flexible, relatively fragile rounds of baked unleavened dough, the tortillas are kept in stacked form, after baking; and cooling, for a given time period of repose to allow the moisture to migrate and be distributed evenly. The tortillas are then unstacked and separated before being further processed into, for instance, taco shells or tostadas.
It is with tortillas that the present invention will be herein disclosed, but the device and method taught herein can be used on other stacked articles that are flat and preferably, but not necessarily, flexible.
With tortillas, the stacking, which is generally automatic, occurs after the unleavened dough has been shaped into flat, round shapes of, for instance, 0.03" to 0.20" thick, and 4" to 14" in diameter, baked, and cooled. A typical stack has 12 tortillas. U.S. Pat. Nos. 4,006,831; 4,938,126 and 5,118,515, among others, discuss such tortilla processing and stacking and are incorporated herein by reference.
Where the stacks are individually packaged and then distributed for use by the ultimate consumer, no further factory processing occurs.
In other instances, however, the tortillas continue to be factory processed; for instance, into taco shells or tostadas, by passing the tortillas in spread-out form, separate from one another, on a moving metallic belt, through a vat of hot oil, as shown for instance in U.S. Pat. No. 4,184,418.
Such stacking and repose, prior to further factory processing, is necessary to redistribute the moisture within the tortilla and allow the moisture to migrate uniformly throughout the tortilla. The tortilla, after coming through the baking process and before stacking, is relatively dry on the surface. Without distributing the moisture evenly throughout the tortilla, blistering within the tortilla occurs when the tortilla is submerged into the hot oil. The pockets of moisture rapidly expand under the influence of the heat in the oil.
Such stacking and period of rest, or repose, during which the stack of tortillas may or may not be shrink-wrapped, can extend from 45 minutes to two hours or more.
In the prior art, the stacks of tortillas were then manually separated one by one and placed on a moving belt. Generally, at least two people were needed on a feed line, and their output was relatively limited. For instance, two people could feed approximately 800 lbs. of tortillas per hour. With the present invention, one person operating the machine can teed 1150 lbs. of tortillas per hour. In terms of actual tortillas, 27,600 tortillas per hour can be handled by the machine shown and described herein.
The present invention repetitively and continuously takes the topmost tortillas from a stack and moves it to a moving belt, so the tortillas are separate from one another. The belt moves the tortillas on for further processing, for instance to produce a taco shell or a tostada.